Incidents of turbulence doubled over summer compared to the previous quarter and were well above the historical five-year average, the Australian Transport Safety Bureau (ATSB) says.

Between October and December there were more than 120 reports of turbulence involving high-capacity aircraft, which the ATSB says was an unprecedented rise.

"It's a little bit cyclical, so every summer we get more turbulence events reported to us, but in this particular summer we had a doubling of the numbers that came in," ATSB research team boss Dr Stuart Godley said

Turbulence occurs when air masses with different speeds, directions or temperatures meet each other.

Dr Godley says it is difficult to say at this stage what caused the turbulence increase.

"The ATSB monitors occurrence reports four times a year, so we look at the past quarter. So we'll be carefully monitoring this over the next quarter, and also over the coming years as well to see whether it keeps increasing."

The ATSB is concerned about the rise because turbulence is the leading cause of in-flight injury.

"Cabin crew are often walking around and often bear the brunt of injuries," Dr Godley said.

"But also passengers that are not wearing their seatbelts can get thrown out of their seat.

"We've had head injuries from people hitting the overhead lockers; we've had broken legs, fractured vertebrae, broken wrists, that sort of thing and also just cuts and abrasions."

Dr Godley says if there is a sustained increase in turbulence, it could lead to changes in flight scheduling.

"Airlines don't want to go through turbulence - they don't want their passengers injured and their cabin crew injured, so they'll do as much as they can to avoid turbulence and to be safe when they do hit it accidentally," he said.

The ATSB says the increase is a good reminder for people to ensure they have their seatbelt fastened throughout their flight.